Electrolysis of alkaline chloride solutions



1966 J. SCHUCKER 3,268,427

ELECTROLYSIS OF ALKALINE CHLORIDE SOLUTIONS Filed Aug. 30, 1962 IJV'WN T018 JwzF 501752155 ZW Z ATTORNEYS United States Patent 3,268,427 ELECTROLYSIS OF ALKALINE CHLORIDE SOLUTIONS Josef Schiicker, Dortmund, Germany, assiguor to Friedrich Uhde G.m.b.H., Dortmund, Germany, a company of Germany Filed Aug. 30, 1962, Ser. No. 220,571 6 Claims. (Cl. 204-125) This invention relates to a process for the electrolysis of alkaline chloride solutions in anelectrolysis cell with a liquid cathode and adjustable anodes.

The voltage of the electrolysis cells can exercise an appreciable influence on the economy of the electrolysis of alkaline chloride solutions, as the cell voltage represents a measure for the specific power consumption. The cell voltage is equal to the product of the distance between the electrodes and a factor which can experimentally be determined for each electrolysis cell and current density. From this dependency it can be expected that the cell voltage will be lowered by reducing the distance between the electrodes, i.e., by placing the anodes closer to the cathode.

Special efforts are therefore made to keep this distance as small as possible and to place the bottom surface of the anodes just above the cathode. The fact that, during cell operation, this distance increases owing to normal wear-and-tear, has lately been compensated for by using adjustable anodes and by adjusting them, from time to time, by hand or by automatic or semi-automatic devices, for the purpose of obtaining as small a distance as possible when using the customary current densities of up to approximately 5000 amps./m. cathode surface, i.e., to keep the bottom surface of the anode, during operation, at an optimum distance above the level of the mercury which, for instance, serves as cathode. In this case, however, disadvantages Which adversely affect either the economy, the purity of the product or the operating safety, must be endured.

It is the object of this invention to provide a proven, new process for the electrolysis of alkaline chloride solutions by means of electrolysis cells with liquid cathode and adjustable anodes.

In particular, it is the object of this invention to provide a process for the electrolysis of alkaline chloride solutions which shows a considerably higher current efficiency than that of the known processes.

It is a further object of this invention to provide a process of electrolysis which is distinguished by high operating safety and by small expense for the adjustment of the anodes.

Other objects of this invention will be evident from the following description, example and drawing wherein:

FIGURE 1 is a section of an electrolysis cell which is illustrative of the prior art;

FIGURE 2 is a section of an electrolysis cell in accordance with the present invention; and

FIGURE 3 is a detail in section of the anode of FIG- URES 1 and 2.

It has been found that electrolysis of alkaline chloride solutions can be carried out particularly advantageously by loading the anodes with a higher current density than is customary and by intentionally immersing the anodes during operation into the liquid cathode. It became unexpectedly obvious that, by using sufiiciently high current densities, the anodes can be brought to the cathode surface down to zero and even be immersed into the cathode without causing a short-circuit between anode and cathode. By this method, current densities from 7,000 to 20,000 and more amps/m. cathode surface are used, enabling an immersion of 0.2 to 5 mm. of the anodes into the cathode whereby the smaller depth of immersion refers to the lower current density.

This remarkable feature can be explained by the fact that the very small chlorine gas bubbles generated on the underside of the anode form, under the particular conditions of this process, together with the brine a stable dispersion which covers the entire anode surface with a thin film thus preventing a short-circuit. Thorough tests proved that in this process, as a result of the rising of the specifically lighter dispersion, fresh brine is constantly drawn into the space between electrodes which ensures the continuity of the process.

The special advantage of this process resides in the fact that the cell voltage, in spite of the high current density, is not higher than is the case with cells which are operated with the customary current densities of up to approximately 5000 amps/m. cathode surface. Moreover, it became evident that electrolysis cells which operate according to the process of this invention have a lower cell voltage than the customary cells, even if the distance between the electrodes of these cells is zero. In the process according to this invention the average voltage decrease amounts to approximately 15% which corresponds to an equally large saving in power consumption or a considerable increase of current efficiency.

Another advantage of the process according to this invention resides in the fact that, to a large extent, the frequent adjustment of the anodes which formerly was necessary in order to maintain the optimum distance between the electrodes is done away with. A decrease of the depth of immersion of the anodes in the liquid cathode has a much smaller elfect on the current efliciency than is the case in the hitherto existing processes.

In this process, it is expedient that the thickness of the liquid cathode stream is approximately double the immersion depth of the anodes. The application of the process can be particularly advantageous, if the side of the anodes facing the cathode is provided with grooves and in addition thereto with discharging holes. Apart from the fact that with this arrangement the effective anode surface is increased, the gas-brine dispersion can rise more easily and thus the flux of the fresh brine to the space between the electrodes be secured.

The process according to this invention cannot only be applied to horizontal electrolysis cells, but also to those with a vertical or inclined cathode.

In the following example, the advantage of the process according to this invention is shown and the method of execution described. This does not mean, however, that the process of this invention is limited to the form of execution described in the example, as it is obvious that it can also be carried out with solutions of other alkaline salts in electrolysis cells of a different construction.

Example In the drawings, FIG. 1, which illustrates the operational position of prior art apparatus, shows the position of the apparatus of this invention prior to operation. The electrolysis of an aqueous solution of sodium chloride with an NaCl content of 310 g./l. is carried out in an electrolysis cell 2 (FIGURE 2) which consists of a blank cell bottom 4, rubberlined side walls 5 are screwed-on boxes 6 at both ends as well as a steel cover 7, rubberlined on the underside and provided with openings for the adjustable anodes 8. The slightly sloping bottom carries a flowing mercury cathode 3 of an average stream thickness of 4 mm. Graphite anode plates 10 (FIGURE 3) on their underside provided with parallel grooves 12 of 3 mm. width, 40 mm. depth, 10 mm. interdistance, and vertical holes 11 of 3 mm. diameter ending in the grooves, pass with their adjustable anode rods through the cover 7 of the cell. Then, for operation according to this invention, the anodes 8 are lowered until the distance to the cathode surface is 4 mm. The cell operates with a voltage of 4.2 v. The amperage is 40,000 amps. so that a current density of 4,000 amps./m. cathode surface results. Per day 1.2 tons of chlorine gas are obtained at the graphite anode and 0.79 ton of sodium as amalgam at the mercury cathode.

In order to carry out the process according to this invention as shown in FIGURE 2, the amperage is increased to 80,000 amps. and the anodes 8 are immersed 1 mm. intothe mercury cathode 3. The cell voltage which amounted to 5.3 v. before the immersion of the anodes, drops to 4.4 v. From this cell 2.4 tons chlorine gas per day are obtained at the anode and 1.58 tons of sodium per day at the cathode.

I claim as my invention:

1. A process for the electrolysis of alkaline chloride solutions in electrolysis cells with adjustable anodes and a liquid cathode comprising immersing the anodes into an alkali electrolyte and the liquid cathode, and applying 2 cur-rent densities of more the 7,000 amps/n1. cathode surface.

2. The process of claim 1 in which the anodes are immersed 0-5 mm. into the liquid cathode.

3. The process of claim 2 in which the thickness of 25 the liquid cathode is double the immersion depth of the anodes.

4. A process for the electrolysis of alkaline chloride solution in electrolysis cells having an anode and a liquid cathode comprising immersing in the liquid cathode at least the surface of the anode which is adjacent thereto, supplying alkaline chloride solution into the interface between the liquid cathode and the surface of the anode immersed therein, applying current densities of a high enough magnitude to generate a stable dispersion of gas in the solution to fill the interface, and removing the dispersion from the interface at a rate corresponding to the supplying of alkaline chloride solution into the interface.

5. The process of claim 4 in which the current densities range between 7,000 amps/n1. and 20,000 amps./m. cathode surface.

6. The process of claim 4 in which the dispersion is removed from the interface through a plurality of passages provided in the anode.

References Cited by the Examiner UNITED STATES PATENTS 2,328,665 9/1943 Munson 204250 2,537,304 1/1951 Condit 204220 2,836,551 5/ 1958 Heller et al 204-220 JOHN H. MACK, Primary Examiner.

MURRAY 'HLLMAN, Examiner.

L. G. WISE, H. M. FLOURNOY, Assistant Examiners. 

1. A PROCESS FOR THE ELECTROLYSIS OF ALKALINE CHLORIDE SOLUTIONS IN ELECTROLYSIS CELLS WITH ADJUSTABLE ANODES AND A LIQUID CATHODE COMPRISING IMMERSING THE ANODES INTO AN ALKALI ELECTROLYTE AND THE LIQUID CATHODE, AND APPLYING CURRENT DENSITIES OF MORE THE 7,000 AMPS./M.2 CATHODE SURFACE. 